Yes I think expanding to flash would be a good move.
I would think Hulu, Crackle, Fearnet ect could utilize the platform
We have all of our content in Flash H264 Video right now to support our main flash based sites. I would love to see Roku support Flash Video if it could actually stream through rtmp from Flash Media Server. If you just mean being able to playback flash encoded video from a file server the way it plays regular H.264 files then that might still be useful so we don't have to encode an additional file but still means we are setting up a parallel servers.
Any word on if Roku plans on releasing any type of FLV container?
Which particular codecs do you need for FLV? Anything beyond h.264/AAC?
Not sure what codecs their FLV is in, I would have to research that.